Numerous compositions, ranging from use in cosmetic to food to industrial and other applications, include ascorbic acid. The problem is that ascorbic acid is unstable, especially in solution, and carbon dioxide (among other things) is generated when ascorbic acid degrades. This degradation process occurs faster when the composition is exposed to higher temperature and can cause the compositions to spoil or change color or otherwise be unfit for consumption or use. Additionally, packaging for the composition often fails due to the pressure generated by the degradation process. This is a costly problem for many industries and is a particular issue for compositions which contain at least about 0.1% by weight ascorbic acid. It is to be understood that all percentages given in this specification are by weight unless otherwise noted.
In the prior art, there are several methods used to slow the degradation of ascorbic acid. Each of the following and any combination thereof have been used: reducing the availability of oxygen, reducing the pH of the composition, adding oxygen scavengers, labeling the compositions with accelerated expiration dates, and storing in controlled climates such as under refrigeration. While these methods work up to a point, none have been sufficient in preventing ascorbic acid degradation.
The degradation of ascorbic acid, especially in solution, is inevitable. Color change is a concern because an ascorbic acid composition will darken over time, at times even before the consumer purchases the composition. A greater concern is the generation of carbon dioxide, which this invention addresses. Carbon dioxide is a direct result of the degradation of ascorbic acid. Since the degradation is accelerated at elevated temperatures, shipping under uncontrolled temperatures may lead to accelerated carbon dioxide generation. Packaging the compositions in air tight containers helps prevent oxygen from degrading the ascorbic acid; however, this packaging can cause an undesirable buildup of carbon dioxide. This buildup may cause premature package failure, or create a pressurized composition, which foams upon opening, resulting in loss of composition.
Furthermore, if a composition is shipped over long distances, such as overseas, the degradation problem is often exacerbated because of the inability to control temperatures during transit. The length of transit time also reduces the shelf life for the composition after transit and causes further degradation of the composition resulting in the excess production of carbon dioxide.
Many of the compositions, which include ascorbic acid, are packaged in glass, vial type containers with a bulb, usually comprised of rubber, and a bulb cap (unlike a service cap, the bulb cap has a hole in the center in which the bulb is located) or a service cap with no bulb. This package type is intended to be an airtight environment, which is considered to be ideal for packaging ascorbic acid-containing compositions. Rubber and other impermeable materials are commonly used in this packaging because they prevent oxygen from contacting the composition. As ascorbic acid breaks down, one of the by-products of the reaction is carbon dioxide. Carbon dioxide gas can build up in these bulbs, causing bulb expansion and package failure. The rate of production of carbon dioxide is rapid and creates problems with maintaining the package's integrity. The consumer sees the bulb expand with carbon dioxide and finds it cosmetically unappealing and evidence that the product has surpassed its shelf life and is no longer acceptable for use.
In some compositions, the carbon dioxide will dissolve back into the composition and create a “carbonated effect” that foams excessively on opening. This is especially true when a service cap is used in place of the rubber bulb.
Those skilled in the art recognize that ascorbic acid breaks down in the presence of oxygen (aerobic). A lesser known pathway is one in which no oxygen is present (anaerobic). Regardless of the pathway, the degradation occurs and carbon dioxide is generated. This challenges the conventional wisdom that ascorbic acid degradation can be slowed or stopped by removing oxygen or adding oxygen scavengers. The anaerobic pathway is evidence that ascorbic acid degradation will occur regardless of the presence of oxygen. Both pathways will yield carbon dioxide and eventually lead to excess gas generation and package failure without a method to address the carbon dioxide generation.